This invention relates, in general, to power management, and more specifically, to power management for multiple satellite systems.
Satellites are becoming important links for communication between stations at different locations throughout the world, particularly for mobile communication stations. For a satellite system to give worldwide coverage, a network or constellation of satellites having polar orbits is desirable. Such a satellite system requires low orbits to allow connection with low power mobile stations.
Each satellite within such a satellite constellation is comprised of many directional antenna cells. Combined, these cells create an umbrella of coverage by the satellite. As the satellites in the constellation orbit within the constellation toward the poles, the umbrella of coverage of the satellites begin to overlap. The closer to the poles the satellites get, the greater the overlap. Cells from one satellite will overlap cells from another satellite resulting in redundancy of coverage. When such an overlap occurs, cells from a satellite having an area of coverage directly beneath the satellite are easier to operate than cells covering the same area from a satellite at a distant angle from the coverage area.
As the satellites within the constellation orbit the earth, they are frequently shadowed from the sun by the earth. Since the power to operate the satellites is generated by solar panels, storage cells, or batteries, are required to store energy for use during "dark" periods or high power demands. In a worst case scenario, any given satellite within the constellation would be shadowed by the earth for approximately 35% of the satellite's orbit. At best, each satellite will be in full view of the sun throughout the satellite's orbit 30% of the time. Each satellite evolves through an annual cycle having a fairly equal distribution of best/worst cases.
In order to efficiently utilize the power of the overlapping satellites allowing storage for "dark" periods as well as for high power demand periods, a power management system is required.